Asymmetric bandwidth allocation

ABSTRACT

A method of determining the position of the split between uplink and downlink bandwidth, in a point of multipoint radio access system with time division duplex scheme comprising a certain number of user terminals and a base station has been disclosed, wherein there are at least two quality of service classes, a first class for guaranteed services (RT) and a second class for not-guaranteed/best effort services (BE). The MAC layer evaluates and controls a further movement of the split—as that initially determined by a Call Admission Control (CAC)—according to the behaviour of uplink and downlink not-guaranteed/best effort queues observed during a certain observation period.

FIELD OF THE INVENTION

[0001] The present invention relates to the field of thepoint-to-multipoint fixed radio access systems adopting the TimeDivision Duplexing (TDD) scheme with time division multiplex access(TDMA) but is applicable to other multiplexing techniques such frequencyor code division multiplex access (FDMA, CDMA). The invention concernsthe Medium Access Control (MAC) layer for providing an efficient way toshare the radio link capacity.

BACKGROUND OF THE INVENTION

[0002] Point-to-multipoint fixed radio access systems consist of onebase station, which is the central unit, and multiple User Terminalsthat exchange data with the base station. Usually a fixed length framestructure is used and, within such frame, uplink and downlink capacityis dynamically allocated.

[0003] The layer architecture of these systems consists of a PhysicalLayer, Medium Access Control (MAC) layer, a Convergence Layer (CL) anduser layers. The main function of MAC layer is the radio resourcemanagement. Not all subscriber terminals, which share the upstreamperiod on a demand basis, can transmit at the same time successfully asthey can in a dedicated-medium situation. The base station MAC protocoldetermines who transmits and when, providing the appropriatetransmission capacity.

[0004] Two basic duplexing methods can be supported bypoint-to-multipoint radio access systems: Time Division Duplex (TDD) andFrequency Division Duplex (FDD). The nature of the traffic being carriedinfluences the choice of the duplex scheme.

[0005] The FDD provides two-way radio communication using paired radiofrequency bands: one band for the transmission in the forward link, theother for the transmission in the reverse direction. For practicalreasons, once the bandwidth dedicated to the two channels has been set,an immovable boundary in frequency/bandwidth is consequently set. Thesepaired bands typically are of equal capacity. If the uplink/downlinkbandwidth needs vary with time, sometimes the bandwidth will be wasted(low demand), and sometimes it will be inadequate (high demand). So thistechnique is ideal for symmetric communications in which the informationflows in both directions are comparable in terms of capacity.

[0006] The TDD transmission technique requires a single carrier for fullduplex communications. Transmit/receive separation occurs in the timedomain as opposed to the frequency domain. Transmission directionalternates between downlink and uplink using a repetitive framestructure. Within such structure, the capacity of the carrier is dividedbetween downlink and uplink transmission in direct proportion to thedesired throughput. A 50% distribution between downlink and uplink timeslots results in a symmetric, full duplex throughput. Moving the timeboundary between downlink and uplink results in an asymmetric throughputand in an efficient accommodation of the channel requirements for burstydata traffic.

[0007] Summarising:

[0008] FDD can adequately handle traffic that has relatively constantbandwidth requirements in both communication directions. On the otherhand, TDD better manages time-varying uplink/downlink traffic because ofthe nature itself of the duplex scheme, which matches the trafficbehaviour.

[0009] When the ratio between the allocated downlink frame portion andthe uplink one varies in time, the TDD scheme is called dynamic oradaptive. The utilisation of adaptive TDD in fixed radio access systemsinvolves an efficient use of the available spectrum when asymmetric andunpredictable traffic represents a considerable percentage of thetraffic load of the system. Such dynamic TDD scheme has been depicted inFIG. 1. It is seen that the frame length comprises a fixed number ofslots but that the split between up and downlink traffic varies.

[0010] Document “MAC Proposal for IEEE 802.16.1”, IEEE 802.16.1mc-00/10of 2000-02-25 discloses a broadband communication standard proposal thatmakes use of TOD and various quality of service classes (QoS).

[0011] According to the above document, when a fixed radio access systemadopts a dynamic TDD scheme, the split between uplink and downlink is asystem parameter that is controlled at higher layers and that depends onthe adopted Call Admission Control policies within the system. When theTDD split changes this is communicated to the MAC layer from higherlayers via the control Service Access Point (SAP). Hence, the splitmovement is driven by services requesting bandwidth guarantees that theCAC takes care of.

[0012] For the above known point to multipoint fixed radio access TDD,the main function of the Medium Access Control (MAC) layer is the radioresource management. The Call Admission Control functionality resides ata higher layer (Network layer).

[0013] The Call Admission Control determines periodically the amount ofbandwidth devoted to the uplink and downlink transmission. The MAC layerfollows the information on the amount of bandwidth devoted to the uplinkand downlink transmission coming from the Call Admission Control andallocates the uplink slots frame by frame to the different userterminals and the downlink slots frame by frame to the downlink traffic(traffic from the Base Station towards the user terminals). The Maclayer does its job without modifying the uplink/downlink amount ofbandwidth, i.e. the position of the split once having been decided bythe Call Admission Control is not moved by the Mac layer.

[0014] The known allocation procedure can be summarised by the followingsteps:

[0015] 1. Periodically the Call Admission Control (CAC) analyses theguaranteed uplink and downlink traffic.

[0016] 2. The Call Admission Control (CAC) evaluates the position of thesplit according to the guaranteed uplink and downlink traffic behaviour(if there have been no significant changes in the traffic the splitposition remains the same evaluated the period before).

[0017] 3. The Call Admission Control (CAC) signals the information onthe split position to the MAC layer.

[0018] 4. The Mac layer allocates the resources frame by frame to theUser terminals and to the Base station using its scheduling policy butalways according to the amount of bandwidth devoted to the uplink anddownlink transmission corresponding to the split evaluated at step 2.

[0019] The above TDD scheme does not take in consideration, for decidingthe downlink/uplink split movement, the behaviour of the Best Efforttraffic (or in general not guaranteed traffic). The term Best Effortrefers to non real time services, usually-Internet services such as WebBrowsing, E-mailing, FTP (File Transfer Protocol) and file sharing.

[0020] In the last few years, the demand in capacity for the latter typeof services has increased substantially. Every category of user nowwants Internet access as a basic service and the number of Internetconnections continues to rise exponentially. If Internet access is theprime interest for a majority of customers then traffic will be verybursty and the overall downlink/uplink capacity ratio in the system mayvary considerably.

[0021] In known dynamic TDD systems the bandwidth allocated to the besteffort traffic is usually a fixed quantity that reflects the expectedload of the Best Effort traffic evaluated only once during thedimensioning phase of the system. In this way the significant andunpredictable variations in time of the Best Effort traffic are notconsidered, and so it may happen that the downlink suffers of a lack ofbandwidth, while the uplink is not using part of its allocated one, orvice versa.

[0022] Prior art document U.S. Pat. No. 5,602,836 shows a method fordynamically allocating bandwidth between up and downlink traffic in aTDMA system. The partition, also called split, between up and down-linkslots in each frame is regulated, although the total number of slots areremains fixed for every frame. When few users use the system in relationto full capacity, the system operates like fixed partition TDD systemswith equal up- and down-link slots in each frame. However, if thetraffic in either direction exceeds half the available slots, thelocation of the split is adapted to the demand. If more than half theavailable slots are required in both directions, the split is set tohalf the available slots in both directions. The system adapts acircular interleaving method for separate queues for up and downlinktraffic.

[0023] U.S. Pat. No. 5,768,254 shows a system aiming at reducing therunlength of dropped packets or the co-channel interference usingadaptive TDD.

SUMMARY OF THE INVENTION

[0024] It is a first object of the invention to adequately respond tonot-guaranteed traffic bandwidth requirements variations by a dynamicTDD scheme compatible with higher layer basic split decisions.

[0025] This object has been accomplished by the subject matter of claim1.

[0026] It is another object of the invention to provide monitoring ofbest effort queues.

[0027] This object has been achieved by the subject matter according toclaim 2.

[0028] It is another object of the invention to provide a set ofparameters useful for determining the split position.

[0029] This object has been achieved by the subject matter according toclaim 3.

[0030] It is another object to provide a further movement of the splitmaking the percentage of losses/wastes in downlink and in uplinkcomparable, i.e. applying a sort of fairness criteria.

[0031] This object has been achieved by the subject matter according toclaim 4.

[0032] It is another object of the invention to provide a preferredprocedure for the evaluation of the uplink and downlink bandwidth valuesin case the amount of bandwidth required by the guaranteed services isless than the total available system bandwidth.

[0033] This object has been achieved by the subject matter according toclaim 5.

[0034] It is another object of the invention to provide a preferredprocedure for the evaluation of the uplink and downlink bandwidth valuesin case a certain amount of bandwidth is left free by higher layers inorder to compensate the instantaneous peak variations of the guaranteedservices.

[0035] This object has been achieved by the subject matter according toclaim 6.

[0036] Further advantages will appear from the following detaileddescription of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 shows a known frame format for asymmetric bandwidthallocation,

[0038]FIG. 2 shows an example of bandwidth partition within a frame,

[0039]FIG. 3 shows an overview of the system according to the invention,

[0040]FIG. 4 shows various definitions regarding an exemplary bandwidthpartition within a frame,

[0041]FIG. 5 shows best effort downlink queues monitored according tothe invention,

[0042]FIG. 6 shows best effort uplink queues monitored according to theinvention,

[0043]FIG. 7 shows a graphical example of other defined variables usefulfor the split movement evaluation according to the invention,

[0044]FIG. 8 shows an example of the split movement according to theinvention

[0045]FIG. 9 shows a first preferred routine for determining the furthermovement of the split according to the invention in case the freebandwidth is exclusively devoted to satisfy the not-guaranteed servicesbandwidth requests, and

[0046]FIG. 10 shows a second preferred routine for determining thefurther movement of the split according to the invention in case thefree bandwidth is devoted at first to compensate the instantaneous peakvariations of guaranteed services and then to satisfy the not-guaranteedservices bandwidth requests.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0047] The invention concerns a point to multipoint radio access systemwith time division duplex scheme using a frame format of fixed duration.

[0048] The system operates with at least two quality of service (QoS)classes; a class of guaranteed service, adapted for real time servicessuch as speech, in the following denoted RT, and a class ofnon-guaranteed/best effort service, in the following denoted BE,suitable for file transfer, e-mail, etc.; i.e. services which may endurea delay.

[0049] The slots in a given frame are allocated to BE downlink traffic,RT downlink traffic, BE uplink traffic and RT uplink traffic, accordingto the classes priority and to uplink and downlink requests of eachclass. One exemplary allocation of the slot assignment for a given framehas been shown in FIG. 2.

[0050] In FIG. 3 an overview of the system has been given. The systemcomprises a Base Station (BS) and a certain number of User Terminals(UT1, UT2, UT3). At the Base Station and at each User Terminal thetraffic flows, according to their QoS requirements, are buffered in theRT and BE queues.

[0051] The base station MAC (medium access control) layer hasinformation on the status of the uplink and downlink queues, since inthe considered systems the User Terminals transmit the information oftheir queues states to the Base Station.

[0052] The present invention relies on information present at the MAClayer on the status of the Best Effort queues and on the informationcoming from higher layers in order to provide a smarter splittingbetween uplink and downlink. Such further splitting makes the systemcapable of following the Best Effort traffic variations avoiding wasteof bandwidth and without modifying neither the fixed bandwidthallocation for the Best Effort services nor the one devoted to the realtime services.

[0053] According to a first step of the preferred procedure, a bandwidthallocation in uplink and downlink is made by the MAC layer, frame byframe, in order to satisfy the requirements of the guaranteed serviceconnections, i.e. the RT traffic accepted by the Call Admission Control,and of a minimal percentage of uplink and downlink bandwidth related tothe expected load of not-guaranteed traffic, i.e. the BE traffic.

[0054] The remaining free slots will be appropriately allocated by theMAC layer, frame by frame according to a second step, whereby notguaranteed services, i.e. BE traffic, and/or instantaneous peakvariations of the guaranteed services, i.e. RT traffic, are allocated.The split between up and downlink free slots devoted to BE/notguaranteed traffic is determined on a frame by frame basis/observationperiod basis.

[0055] As explained above, the number of the total remaining free slotsin the system at a certain instant (after the first step in theallocation procedure) depends on the Call Admission Control decision.The aim of the invention is to use these free slots, dividing thembetween uplink and downlink, in an efficient and dynamic way.

[0056] More specifically, the following steps are carried out in apreferred routine of the invention:

[0057] 1. Periodically the Call Admission Control (CAC) analyses theguaranteed uplink and downlink traffic.

[0058] 2. The position of the split according to the guaranteed uplinkand downlink traffic behaviour is evaluated, whereby if there have beenno significant change in the traffic, the split position remains thesame and if there have been a change in the traffic, the split is moved.

[0059] 3. The call admission control (CAC) signals the split position tothe MAC layer.

[0060] 4. The base station medium access control (MAC) layer monitorsthe status of best effort (BE) uplink and downlink queues averaging themduring an observation period.

[0061] 5. Every observation period, the base station medium accesscontrol (MAC) layer evaluates a further movement of the split.

[0062] 6. According to the evaluated split position, the base stationmedium access control (MAC) layer allocates the resources frame by frameto the user terminals and to the base station using its schedulingpolicy.

[0063] The routine driving the decision on the split movement accordingto the invention shall now be explained.

[0064] Let be:

[0065] S the total radio link capacity

[0066] S^(DL) the total amount of bandwidth allocated to the downlink byhigher layers

[0067] S_(RT) ^(DL) the amount of bandwidth allocated to the not-BestEffort services on the downlink

[0068] S_(BE) ^(DL) the fixed amount of bandwidth allocated to the BestEffort services on the downlink

[0069] S^(UL) the amount of bandwidth allocated to the uplink by higherlayers

[0070] S_(RT) ^(UL) the amount of bandwidth allocated to the not-BestEffort services on the uplink

[0071] S_(BE) ^(UL) the fixed amount of bandwidth allocated to the BestEffort services on the uplink

[0072] The amount of bandwidth not related to any constraints indownlink is equal to

S _(free) ^(DL) =S ^(DL) −S _(RT) ^(DL) −S _(BE) ^(DL)  (1)

[0073] and for the uplink

S _(free) ^(UL) =S ^(UL) −S _(RT) ^(UL) −S _(BE) ^(UL)  (2)

[0074] as shown in FIG. 4.

[0075] Let's define q_(BE) ^(DL)(i) the state of the Best Effort queueinside the Base Station at the i'th frame and q_(BE) ^(UL)(i,p) thestate of the Best Effort queue inside the p'th User Terminal known bythe Base Station at the i'th frame. Then consider: $\begin{matrix}{{q_{BE}^{UL}(i)} = {\sum\limits_{p = 1}^{M}{q_{BE}^{UL}\left( {i,p} \right)}}} & (3)\end{matrix}$

[0076] where M is the number of the User Terminals within the system.

[0077] The behaviour of the Best Effort traffic entering the system ismonitored and the queue states are averaged for a certain period. Thisperiod is called observation period and it is chosen to be an integermultiple of the frame length. So define N as the observation periodlength expressed in frames. Every N frames let's evaluate the averagestate of the queues; for the k'th observation period it will be:$\begin{matrix}{{{\overset{\_}{q}}_{{BE},k}^{DL} = {\frac{\sum\limits_{j = k}^{k + N - 1}\quad {q_{BE}^{DL}(j)}}{N}\quad {and}}}\quad} & (4) \\{{{\overset{\_}{q}}_{{BE},k}^{UL} = {\left\lbrack {\sum\limits_{j = k}^{k + N - 1}{\sum\limits_{p = 1}^{M}{q_{BE}^{UL}\left( {j,p} \right)}}} \right\rbrack/N}}\quad {{{{where}\quad k} = 1},{N + 1},{{2N} + 1},{{3N} + 1},\quad \ldots}} & (5)\end{matrix}$

[0078]FIG. 5 refers to the BE downlink queue state of the Base Station(i.e. the BE traffic load to be sent on the downlink). The x-axis refersto the total quantity of BE data waiting to be sent on the downlink.FIG. 6 refers to the BE uplink queues states of the User Terminals (i.e.the BE traffic load to be sent on the uplink). So in this figure thex-axis refers to the total quantity of data waiting to be sent on theuplink. In FIG. 5 and 6, the y-axis show the past number of executedframes i to i+N−1 (past frames). The executed frames are grouped inobservation periods of N frames.

[0079] The queues for more frames are examined because the system maynot be able to decide the split position efficiently from a frame toframe basis but only over a longer period.

[0080] According to the invention, the queue behaviour is estimated byaveraging the queue state values over every observation period. In anextreme case, if the observation period is equal to one frame, thequeues are examined on a frame by frame basis.

[0081] In FIG. 6, the grey area denoted the double sum corresponds tothe total sum of uplink queues for all User Terminals within a givenobservation period.

[0082] If we compare the above average values in (4) and (5) with theallocated bandwidth during the considered observation period, we obtaina measurement of the average experienced lack or waste of bandwidth inboth directions.

[0083] Let's then define:

diff_(k) ^(DL) ={overscore (q)} _(BE,k) ^(DL) −S _(BE) ^(DL) −S_(free,k) ^(DL)  (6)

[0084] and

diff_(k) ^(UL) ={overscore (q)} _(BE,k) ^(DL) −S _(BE) ^(UL) −S_(free,k) ^(UL)  (7)

[0085] that therefore represent the bandwidth portions of which it wouldhave been necessary to increase or decrease the downlink/uplinkbandwidth in order to satisfy the mean request of BE traffic experiencedduring the k'th observation period by downlink/uplink, as depicted inFIG. 7.

[0086] As shown in FIG. 7, one can note that most of the time, the moredifficult part of the split decision is not where to move it but howmuch to move it. Suppose now to apply a split movement of a quantity Xk,where a positive value of Xk means a split movement towards the uplinkand consequently an increase in S_(free) ^(DL) and a decrease inS_(free) ^(UL), while a negative value of X_(k) means a split movementtowards the downlink and consequently a decrease in S_(free) ^(DL) andan increase in S_(free) ^(UL), as shown in FIG. 8.

[0087] Once having implemented such movement the quantity diff_(k)^(DL)−X_(k) is equal to the average bandwidth portion per frame that thedownlink did not obtain or use while diff_(k) ^(UL)+X_(k) is the averagebandwidth portion per frame that the uplink did not use or obtain.

[0088] The above values represent the predicted losses/wastes for thedownlink and for the uplink if the Best Effort traffic maintains thesame behaviour it had during the last N frames. In order to make thepercentage of losses/wastes in downlink and in uplink comparable, i.e.applying a sort of fairness criteria, the following equation shall beverified: $\begin{matrix}{\frac{{diff}_{k}^{DL} - X_{k}}{{\overset{\_}{q}}_{{BE},k}^{DL}} = \frac{{diff}_{k}^{UL} + X_{k}}{{\overset{\_}{q}}_{{BE},k}^{UL}}} & (8)\end{matrix}$

[0089] from which it follows that: $\begin{matrix}{X_{k} = {{round}{\quad \quad}\left( \frac{{{diff}_{k}^{DL} \times {\overset{\_}{q}}_{{BE},k}^{UL}} - {{diff}_{k}^{UL} \times {\overset{\_}{q}}_{{BE},k}^{DL}}}{{\overset{\_}{q}}_{{BE},k}^{DL} + {\overset{\_}{q}}_{{BE},k}^{UL}} \right)}} & (9) \\{{{{So}\quad {that}},{{{if}\quad {Xk}} > {0\text{:}}}}\left\{ \begin{matrix}{S_{k + 1}^{DL} = {S_{k}^{DL} + {\min \left( {X_{k},S_{{free},k}^{UL}} \right)}}} \\{S_{k + 1}^{UL} = {S_{k}^{UL} - {\min \left( {X_{k},S_{{free},k}^{UL}} \right)}}}\end{matrix} \right.} & (10) \\\left\{ \begin{matrix}{S_{{free},{k + 1}}^{DL} = {S_{{free},k}^{DL} + {\min \left( {X_{k},S_{{free},k}^{UL}} \right)}}} \\{S_{{free},{k + 1}}^{UL} = {S_{{free},k}^{UL} - {\min \left( {X_{k},S_{{free},k}^{UL}} \right)}}}\end{matrix} \right. & (11) \\{{{{if}\quad {Xk}} < {0\text{:}}}\left\{ \begin{matrix}{S_{k + 1}^{DL} = {S_{k}^{DL} - {\min \left( {{X_{k}},S_{{free},k}^{DL}} \right)}}} \\{S_{k + 1}^{UL} = {S_{k}^{UL} + {\min \left( {{X_{k}},S_{{free},k}^{DL}} \right)}}}\end{matrix} \right.} & (12) \\\left\{ \begin{matrix}{S_{{free},{k + 1}}^{DL} = {S_{{free},k}^{DL} - {\min \left( {{X_{k}},S_{{free},k}^{DL}} \right)}}} \\{S_{{free},{k + 1}}^{UL} = {S_{{free},k}^{UL} + {\min \left( {{X_{k}},S_{{free},k}^{DL}} \right)}}}\end{matrix} \right. & (13)\end{matrix}$

[0090] The resulting values S_(k+1) ^(DL), S_(k+1) ^(UL), S_(free,k+1)^(DL) and S_(free,k+1) ^(UL) will be valid for the following observationperiod, the (k+1)th, at the end of which the new bandwidth values arecalculated, using again the formulas (6)-(13).

[0091] The above routine has been shown in FIG. 9.

[0092] Usually, there are two reasons behind the existence of freebandwidth, within the considered systems. The first reason—which istaken into consideration until now—may be that the amount of bandwidthrequired by the guaranteed services is less than the total availablesystem bandwidth. The second reason may be that a certain amount ofbandwidth is left free by higher layers in order to compensate theinstantaneous peak variations of the guaranteed services. Therefore thefree bandwidth that can be used for Best Effort services, as previouslystated, is only the amount that the guaranteed services do not need.

[0093] So, in order to include the latter case, a second routineaccording to the invention is defined as follows:

[0094] The (6) to (9), (11) and (13) remain valid, i.e. the splitmovement Xk and the downlink and uplink free bandwidth S_(free,k+1)^(DL) and S_(free,k+1) ^(UL) are evaluated in the same manner once inevery k'th period;

[0095] The formulas (10) and (12) instead are evaluated frames by framein the following way: $\begin{matrix}\left\{ \begin{matrix}{S_{i + 1}^{DL} = {S_{i}^{DL} + {\min \left( {X_{k},{S_{{free},i}^{UL} - S_{{comp},i}^{UL}}} \right)}}} \\{S_{i + 1}^{UL} = {S_{i}^{UL} + {\min \left( {X_{k},{S_{{free},i}^{UL} - S_{{comp},i}^{UL}}} \right)}}}\end{matrix} \right. & (14) \\\left\{ \begin{matrix}{S_{i + 1}^{DL} = {S_{i}^{DL} - {\min \left( {{X_{k}},{S_{{free},i}^{DL} - S_{{comp},i}^{DL}}} \right)}}} \\{S_{i + 1}^{UL} = {S_{i}^{UL} + {\min \left( {{X_{k}},{S_{{free},i}^{DL} - S_{{comp},i}^{DL}}} \right)}}}\end{matrix} \right. & (15)\end{matrix}$

[0096] where S_(comp,i) ^(DL) and S_(comp,i) ^(UL) represent the amountof bandwidth used at the i'th frame by the guaranteed services tocompensate their instantaneous peak variations, i=k, k+1, . . . k+N−1 isthe current frame and k=1, N+1, 2N+1, . . . is the current observationperiod. The above routine has been shown in FIG. 10.

[0097] The advantages of the present invention can be summarised asfollows:

[0098] If the Best Effort/not-guaranteed traffic is highly asymmetric,the proposed TDD has a significant gain on the BestEffort/not-guaranteed throughput and traffic losses with respect toknown systems.

[0099] Even if the Best Effort/not-guaranteed traffic experienced by thesystem is only slightly asymmetric, the proposed TDD has a certain gainon the system Best Effort/not-guaranteed throughput with respect to theclassical dynamic TDD.

[0100] The proposed TDD reduces considerably the amount of unusedbandwidth with respect to known systems.

[0101] According to the invention, the total Best Effort/not-guaranteedpacket loss probability of the system is minimised.

[0102] Since the invention makes use of a simple monitoring of the BestEffort/not-guaranteed queues, it can be easily implemented in existingsystems.

[0103] Moreover, the preferred embodiments of the invention arecompatible with uplink-downlink bandwidth split decisions taken athigher layers.

[0104] The invention is also applicable to systems using retransmissionmechanisms of lost packets. In this case, the throughput gain of theinvention becomes even more conspicuous in relation to known TDDsystems.

[0105] Finally, it can be noted that since the allocated bandwidth iscontrolled according to the various queue states, not only a gain interms of throughput but also a decrease of packet delay have beenaccomplished.

1-6. (canceled)
 7. A method of determining and effectuating splitpositions between uplink and downlink bandwidth in a point to multipointradio access system, wherein the system utilizes a time division duplexscheme on a frame by frame basis and with at least two quality ofservice classes, a first class for guaranteed services (RT) and a secondclass of best effort services (BE); wherein, within every frame aportion of bandwidth is devoted to uplink traffic and another portion todownlink traffic, and wherein a split between uplink and downlinkbandwidth is controlled by a call admission controller (CAC), andwherein scheduling of traffic is performed according to a schedulingpolicy carried out by a medium access control (MAC) layer, said methodcomprising the steps of: said medium access control (MAC) layermonitoring the status of best effort (BE) uplink and downlink queues andaveraging them during an observation period; for every observationperiod, said medium access control (MAC) layer evaluating a furthermovement of the split; and according to the evaluated split position,said medium access control (MAC) layer allocating resources frame byframe to user terminals and to a base station using its schedulingpolicy.
 8. The method recited in claim 7, wherein the behavior of thebest effort queues is evaluated by averaging the states of the besteffort downlink queues (q_(BE,k) ^(−DL)) and of the best effort uplinkqueues (q_(BE,k) ^(−UL)) once every observation period.
 9. The methodrecited in claim 8, wherein quantities q_(BE,k) ^(−DL) and q_(BE,k)^(−UL), related to the behavior of the best effort traffic entering thesystem are used to calculate variables diff_(k) ^(DL) and diff_(k)^(UL), representing the bandwidth portion it would have been necessaryto increase or decrease in order to satisfy the mean request of BestEffort traffic experienced during the current observation period bydownlink/uplink, whereby a first quantity (diff_(k) ^(DL)−X_(k)), beingequal to the average bandwidth per frame that the downlink will not useor obtain within the next observation period in case the Best Effortdownlink traffic maintains the same behavior it had in the currentobservation period, is defined, and whereby a second quantity (diff_(k)^(UL)+X_(k)), being equal to the average bandwidth per frame that theuplink will not use or obtain within the next observation period in casethe Best Effort downlink traffic maintains the same behavior it had inthe current observation period is defined, X_(k) being the supposedvalue of the split movement, wherein a positive value of X_(k) implies adecrease of the uplink bandwidth while a negative value of X_(k) impliesa decrease of the downlink bandwidth.
 10. The method recited in claim 9,wherein once evaluated the X_(k) quantity making equal the ratio betweendiff_(k) ^(DL)−X_(k) and the average state of the best effort downlinkqueues (q_(BE,k) ^(−DL)) and the ratio between diff_(k) ^(−DL)+X_(k) andthe average state of the best effort uplink queues (q_(BE,k) ^(−UL)),the further movement of the split being calculated choosing the minimumvalue between |X_(k)| and the available free bandwidth.
 11. The methodrecited in claim 10, wherein the uplink and downlink bandwidth valuesare calculated at the end of every observation period, making use of theevaluated split movement and of the free uplink and downlink bandwidth.12. The method recited in claim 10, wherein the uplink and downlinkbandwidth values are evaluated frame by frame making use of the splitmovement and of the free uplink and downlink bandwidth calculated at theend of every observation period.